全文获取类型
收费全文 | 13612篇 |
免费 | 711篇 |
国内免费 | 7篇 |
出版年
2022年 | 24篇 |
2021年 | 93篇 |
2020年 | 58篇 |
2019年 | 85篇 |
2018年 | 139篇 |
2017年 | 145篇 |
2016年 | 245篇 |
2015年 | 375篇 |
2014年 | 432篇 |
2013年 | 1138篇 |
2012年 | 764篇 |
2011年 | 826篇 |
2010年 | 481篇 |
2009年 | 461篇 |
2008年 | 778篇 |
2007年 | 864篇 |
2006年 | 852篇 |
2005年 | 889篇 |
2004年 | 972篇 |
2003年 | 907篇 |
2002年 | 856篇 |
2001年 | 138篇 |
2000年 | 96篇 |
1999年 | 140篇 |
1998年 | 213篇 |
1997年 | 199篇 |
1996年 | 160篇 |
1995年 | 145篇 |
1994年 | 114篇 |
1993年 | 153篇 |
1992年 | 126篇 |
1991年 | 91篇 |
1990年 | 90篇 |
1989年 | 88篇 |
1988年 | 85篇 |
1987年 | 64篇 |
1986年 | 73篇 |
1985年 | 86篇 |
1984年 | 100篇 |
1983年 | 87篇 |
1982年 | 106篇 |
1981年 | 95篇 |
1980年 | 83篇 |
1979年 | 41篇 |
1978年 | 47篇 |
1977年 | 43篇 |
1976年 | 51篇 |
1975年 | 26篇 |
1974年 | 36篇 |
1973年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Marine annelids in the subfamily Calamyzinae (family Chrysopetalidae) are either symbiotic or free-living forms that have been mainly reported from deep-sea chemosynthetic systems. Symbiotic calamyzines mainly live in the mantle cavity of bivalves in hydrothermal vents or cold seeps, but one species is also found to be inserted into the epidermis of polychaetes. We found a single specimen of calamyzine polychaete on the body surface of Octopus sp. collected in the Sea of Kumano (Japan), which represents the first known record of symbiotic association between polychaetes and octopuses. We described the specimen as Spathochaeta octopodis gen. et sp. nov. Spathochaeta gen. nov. can be discriminated from other genera in Calamyzinae by the presence of spatula-shaped notochaetae and dorsal chaetal lobes. We also provided the phylogenetic position of S. octopodis gen. et sp. nov. within Chrysopetalidae based on four gene markers (COI, 16S, 18S, H3). www.zoobank.org/urn:lsid:zoobank.org:pub:A8FB15C1-31A7-4487-966B-13F10E19A373. 相似文献
102.
103.
104.
105.
Marcos V. V. de Oliveira Xing Jin Xuan Chen Daniel Griffith Sai Batchu Hiroshi A. Maeda 《The Plant journal : for cell and molecular biology》2019,97(5):901-922
l ‐Tyrosine is an essential aromatic amino acid required for the synthesis of proteins and a diverse array of plant natural products; however, little is known on how the levels of tyrosine are controlled in planta and linked to overall growth and development. Most plants synthesize tyrosine by TyrA arogenate dehydrogenases, which are strongly feedback‐inhibited by tyrosine and encoded by TyrA1 and TyrA2 genes in Arabidopsis thaliana. While TyrA enzymes have been extensively characterized at biochemical levels, their in planta functions remain uncertain. Here we found that TyrA1 suppression reduces seed yield due to impaired anther dehiscence, whereas TyrA2 knockout leads to slow growth with reticulate leaves. The tyra2 mutant phenotypes were exacerbated by TyrA1 suppression and rescued by the expression of TyrA2, TyrA1 or tyrosine feeding. Low‐light conditions synchronized the tyra2 and wild‐type growth, and ameliorated the tyra2 leaf reticulation. After shifting to normal light, tyra2 transiently decreased tyrosine and subsequently increased aspartate before the appearance of the leaf phenotypes. Overexpression of the deregulated TyrA enzymes led to hyper‐accumulation of tyrosine, which was also accompanied by elevated aspartate and reticulate leaves. These results revealed that TyrA1 and TyrA2 have distinct and overlapping functions in flower and leaf development, respectively, and that imbalance of tyrosine, caused by altered TyrA activity and regulation, impacts growth and development of Arabidopsis. The findings provide critical bases for improving the production of tyrosine and its derived natural products, and further elucidating the coordinated metabolic and physiological processes to maintain tyrosine levels in plants. 相似文献
106.
107.
Naoshi Yamamoto Sayaka Ohrui Takahiro Okada Tsuyoshi Saitoh Noriki Kutsumura Yasuyuki Nagumo Yoko Irukayama-Tomobe Yasuhiro Ogawa Yukiko Ishikawa Yurie Watanabe Daichi Hayakawa Hiroaki Gouda Masashi Yanagisawa Hiroshi Nagase 《Bioorganic & medicinal chemistry》2019,27(8):1747-1758
Morphinan derivatives lacking the 4,5-epoxy ring were synthesized to examine the participation of the 14-OH group, the 3-OMe group, and the aromaticity of the A-ring in the activity and selectivity for the orexin 1 receptor (OX1R). The assay results and the conformational analyses of the 14-dehydrated and 14-H derivatives suggested that the orientations of the 6-amide side chain and the 17-benzenesulfonyl group would play important roles in the activity for OX1R. In the 6β-derivatives, removal of the 3-OMe group and the reduction of the A-ring significantly decreased the activity toward the OX1R, but these changes did not affect the 6α-derivatives. These results indicate that the 3-OMe group and the A-ring would be essential structural moieties for the 6β-derivatives. 相似文献
108.
The new species Tinocladia sanrikuensis sp. nov. H.Kawai, K.Takeuchi & T.Hanyuda (Ectocarpales s.l., Phaeophyceae) is described from the Pacific coast of the Tohoku region, northern Japan based on morphology and DNA sequences. The species is a spring–summer annual growing on lower intertidal to upper subtidal rocks and cobbles on relatively protected sites. T. sanrikuensis has a slimy, cylindrical, multiaxial erect thallus, slightly hollow when fully developed, branching once to twice, and resembles T. crassa in gross morphology. The erect thalli are composed of a dense medullary layer, long subcortical filaments, and assimilatory filaments of 11–35 cells, up to 425 μm long and curved in the upper portion. Unilocular zoidangia are formed on the basal part of assimilatory filaments. The species is genetically most closely related to T. crassa and has the same basic thallus structures but differs in having thinner and longer assimilatory filaments. DNA sequences of the mitochondrial cox1 and cox3, chloroplast atpB, psaA, psbA and rbcL genes support the distinctness of this species. 相似文献
109.
Ichthyological Research - A new species of perchlet, Plectranthias maekawa, is described on the basis of three specimens (58.2–65.1 mm standard length: SL) from the Tokara Islands,... 相似文献
110.
Ujifuku Kenta Fujimoto Takashi Sato Kei Morofuji Yoichi Muto Hideki Masumoto Hiroshi Nakagawa Shinsuke Niwa Masami Matsuo Takayuki 《Cellular and molecular neurobiology》2022,42(4):997-1004
Cellular and Molecular Neurobiology - Metastatic brain tumors have poor prognoses and pose unmet clinical problems for the patients. The blood–brain barrier (BBB) implication is supposed to... 相似文献